(a) Technical Field
The present disclosure relates to a motor-generator system driven by a V-belt. More particularly, it relates to a motor-generator system driven by a V-belt, which improves power transmission efficiency using a speed controller controlling the rotational speed of the V-belt.
(b) Background Art
An example of a typical V-belt is shown in FIG. 5. A V-belt 6 is connected to a crankshaft pulley 1 of an engine 5, a motor-generator pulley 2, a water pump pulley 3, and a compressor pulley 4. When a crankshaft of the engine 5 rotates, the power of the engine 5 is transmitted to the water pump pulley 3 or the compressor pulley 4 as auxiliary equipment by the V-belt 6. A motor-generator comprises an electric motor and an electric generator. The electric motor rotates the motor-generator pulley 2 to start the engine 5. During traveling of a vehicle, the power of the engine 5 is transmitted to the electric generator via the motor-generator pulley 2, and the generated electricity is stored in a battery (not shown).
A typical relationship between V-belt speed and transmission force is shown in FIG. 6. As shown in FIG. 6, the transmission force of the V-belt depends on the speed of the V-belt, i.e., the rotational speed of the pulley. When the speed of the V-belt is low, i.e., when the rotational speed of the pulley is low, the transmission force of the V-belt decreases, and thus it is impossible to provide efficient power transmission.
A typical relationship between motor rotational speed, torque, and efficiency is shown in FIG. 7. As shown in FIG. 7, the efficiency of the motor is very poor at low speed and high torque. In FIG. 7, if the motor torque is 400 to 500 Nm at a rotational speed of about 250 rpm, for example, the efficiency of the motor is below 50%. In general, this motor torque is inevitably used during start-up of the engine, and thus the load of the battery is increased. Since this low rotational speed corresponds to a V-belt speed of 2 to 5 m/s, the transmission force of the V-belt is as low as 3 kW as shown in FIG. 6.
Japanese Patent Publication No. 2003-42248 discloses a belt tension adjusting device, which applies a large tension to a V-belt to transmit a large transmission torque from a starter motor to a crankshaft of an engine during start-up of the engine and releases the tension after the start-up is complete. However, although the increase in the tension of the V-belt prevents slip between the V-belt and the pulley, it does not improve the power transmission efficiency.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.